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2018 Q50 3.0t Rough Idle & Check Engine Light - O2 Sensor?

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Brittany E. · rep 0 · May 22, 5:11 AM · 1 replies · solved · Question

Vehicle: 2018 Infiniti Q50 3.0t Red Sport

Hey everyone,

I'm experiencing some issues with my 2018 Infiniti Q50 3.0t Red Sport. Lately, I've noticed a rough idle, especially when the car is cold or at a stoplight. It's not constant, but definitely noticeable.

A few days ago, the Check Engine Light (CEL) came on. I haven't had a chance to get the codes read yet, but I'm wondering if this is a common problem for these VR30DDTT engines. The car has about 75,000 miles on it.

Could this be an oxygen sensor issue, or something more serious? What are the typical causes for rough idle and a CEL on this model? Any advice on what I should check first, or what kind of repair costs I might be looking at if it's an O2 sensor or something similar?

Thanks for any insights!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:11 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a common set of symptoms that can point to a few different issues on your 2018 Infiniti Q50 3.0t Red Sport. A rough idle combined with a Check Engine Light (CEL) often indicates a problem with the engine's air-fuel mixture or combustion efficiency.

Here's a breakdown of potential causes and what to do:

  1. Get the OBD-II Codes Read Immediately: This is the crucial first step. Most auto parts stores offer free code reading. Common codes associated with rough idle and air-fuel issues include:

    • P0171 (System Too Lean, Bank 1)
    • P0174 (System Too Lean, Bank 2)
    • P0300 (Random/Multiple Cylinder Misfire Detected) These codes will narrow down the diagnostic path significantly.

  2. Potential Causes:

    • Oxygen (O2) Sensors: These sensors monitor the exhaust gases to help the engine control unit (ECU) maintain the correct air-fuel ratio. A failing O2 sensor can send incorrect data, leading to a rich or lean condition, rough idle, and a CEL. For the VR30DDTT, there are multiple O2 sensors (upstream and downstream).
    • Vacuum Leaks: Unmetered air entering the engine can cause a lean condition and rough idle. Check for cracked hoses, loose connections, or a faulty PCV valve.
    • Spark Plugs/Ignition Coils: Worn spark plugs or failing ignition coils can lead to misfires, causing a rough idle and potentially a P0300 code. Given your mileage, spark plugs might be due for replacement if not done already.
    • Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can provide incorrect air intake readings to the ECU, disrupting the air-fuel mixture.

  3. When to See a Shop:

    • If the CEL is flashing, this indicates a severe misfire that could damage the catalytic converter. Pull over safely and have the vehicle towed to a shop.
    • If you've read the codes and aren't comfortable diagnosing or replacing parts yourself.
    • If the problem persists after checking basic items like air filter or visually inspecting hoses.
    • For complex diagnostics like smoke testing for vacuum leaks or advanced electrical testing of sensors.

  4. Typical Costs (Estimates):

    • O2 Sensor Replacement: Parts can range from $80-$200 per sensor. Labor can add $100-$300, depending on accessibility (some are harder to reach than others).
    • Spark Plugs: Parts around $100-$150 for a set, labor $200-$400 due to the VR30DDTT's engine layout.
    • Vacuum Leak Repair: Highly variable, from $50 for a simple hose clamp to $500+ for complex manifold gasket issues.

Addressing this promptly will help prevent further issues and ensure your Q50 runs smoothly.

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